“But Mr. Eastburn… which ones are the parents?”
This is one of the most common questions that I hear at Riverside Elementary School, where I have worked the past four years teaching science. For as long as anyone can remember (a long time in our collective memory), there has been a captive population of box turtles in our enclosed courtyard, and ever since I started working in the Princeton Public Schools, it has been my mission to learn more about them.
Piecing together stories from a variety of sources, it appears that the original turtles were probably pets that were “dumped” into our courtyard more than 30 years ago. Since that time, others have found their way in, most likely from other families that wanted to give their turtles a safe home. Our school is in a developed part of town, so it is unlikely that any of our reptilian companions wandered in on their own, and turtles don’t usually climb walls. Add to that founding group a handful of babies that we find each fall, and Riverside has managed to sustain a healthy population that grows each year. In fact, it might soon become necessary to find new habitats for some of our turtles; the total population currently stands at 50.
There is one major problem, though. With a population derived from pets that outlived the interest of their captors (which seems to happens quite often), we have a mix of non-native, and possibly native, species. Several individuals look unquestionably like Eastern box turtles, scientific name Terrapene carolina carolina, listed as a “species of concern” in New Jersey. While our population keeps growing, Eastern box turtle numbers across the state are in decline, primarily because of road deaths, habitat loss, and (unfortunately) collection for the pet trade. This last option usually doesn’t end well for the turtle: they wind up malnourished, neglected, or worse.
There is no guarantee, however, that our scaly friends are actually Eastern box turtles, since our population contains two non-native males: Albert, a three toed box turtle, or Terrapene mexicana triunguis, from the southern central United States, and Confetti, an ornate box turtle, or Terrapene ornata, from the Great Plains. Their presence highlights the likelihood that these are all released pets, and raises the possibility of hybridization.
As for the baby turtles we find each year, what are they? Are they Eastern box turtles, or some sort of cross between our mix of species? If they are not completely native, they should all remain in the courtyard, despite our growing population, because they won’t be well adapted to live outside of our safe, protective walls. If, on the other hand, the hatchlings are pure Terrapene carolina carolina, then perhaps we might start releasing our surplus babies into appropriate habitats (if we can find any, that is…).
Which brings me back to the first question, the one that started this post. Every time we find a new turtle, the first question from students relates to who the parents might be. And since turtles don’t invest in maternal (or paternal) care, the babies are left to fend for themselves, and no parent will ever claim their children.
So how can we establish where our hatchlings came from?
Well, it just so happens that I have a background in biology, with a bachelor’s and (nearly) a master’s in the discipline. In fact, another blog I had been keeping until recently was dedicated to my studies of vegetarian jumping spiders in Central America, which is something I do in my spare time. Many of my courses focused on genetics, and it just so happens that we have one of the world’s greatest Departments of Molecular Biology at Princeton University, right across town. In fact, I have made some great contacts at the university, and hope to feature them and their work in future posts. I’ve read up on microsatellites, which are repeating genetic markers used to trace heredity in all sorts of ecological studies, as well as ways to extract turtle DNA. This past summer, I started putting my research into practice, and had a reasonable rate of success.
Microsatellites are used in DNA fingerprinting of all sorts of organisms, including people, and the basic principles are universal among species:
Now comes the real challenge: will my students, in grades kindergarten through fifth, be able to process the data we’ve generated? Will they be able to determine each turtle’s genetic mix?
And here comes the biggest challenge: will they be able to write a scientific paper that can be published in an actual research journal?
From this point forward, this blog will be devoted to that quest, as well as any surprises that we might find along the way!